• Gather all the ingredients.
  

To Prepare the Potatoes

• Peel 2 russet potatoes and cut them into 1½-inch (3.8-cm) pieces; I usually cut each potato into four pieces. Cut the pieces about the same size so that they’ll cook evenly.
  
• Put the potatoes in a medium pot and add cold water to cover by 1 inch (2.5 cm). Add 2 tsp Diamond Crystal kosher salt to the pot and turn on the heat to medium high. Cover with the lid, leaving it slightly ajar to avoid a boilover. Tip: Start cooking the potatoes in cold water to heat them up slowly so they cook through evenly. While you‘re cooking and cooling the potatoes, prepare the other ingredients (see the next section).
  
• Once the water is boiling, remove the lid and reduce the heat to medium. Cook on a gentle boil until a skewer pierces a potato smoothly, about 15 minutes.
  
• Drain the water completely from the pot using the lid to hold back the potatoes. Put the pot with the potatoes back onto the stove over medium heat to evaporate any remaining water completely, shaking the pot constantly to avoid sticking. When there is no liquid left, remove the pot from the heat.
  
• Mash the potatoes lightly, leaving some small chunks for texture. Transfer the potatoes to a large bowl.
  
• While the potatoes are hot, toss with 1 Tbsp rice vinegar (unseasoned) and freshly ground black pepper. Set aside to cool. Tip: Why not add mayonnaise here? Because the mayo will separate if you add it to hot potatoes. Therefore, work on the other ingredients while the potatoes cool down.
  

To Prepare the Other Ingredients

• While the potatoes are cooking and cooling, prepare the other ingredients. Bring a small pot of water to a boil for cooking the carrots and corn (next step). Peel and cut 2 inches carrot in half or quarters lengthwise, and then cut crosswise into thin slices. You may use a mandoline slicer to cut it thinly.
  
• Once the water is boiling, cook the carrot slices and ¼ cup (40 g) frozen corn for 5 minutes. If you‘re using canned corn, you don‘t need to boil it.
  
• Alternatively, you can use the microwave to heat the carrot for a few minutes until a skewer pierces it smoothly; don’t overcook it or the carrot will get mushy. Drain the water in a fine-mesh sieve and set aside to cool.
  
• Add 1 large egg (50 g each w/o shell) to the same pot and add enough cold tap water to cover by 1 inch (2.5 cm). Turn on the heat to medium and bring to a boil. Once boiling, set a timer for 11–12 minutes and reduce the heat to maintain a gentle simmer. When the timer goes off, shock the egg in cold water until cool.
  
• Peel the boiled egg and chop it into smaller pieces. Set aside.
  
• Peel 1 Persian cucumberleaving some skin on to create a striped pattern, and thinly slice it crosswise. Tip: If you‘re using a large cucumber, you may need to cut it in half or quarters lengthwise before slicing it.
  
• Sprinkle ½ tsp Diamond Crystal kosher salt over the cucumber slices, knead them with your hands, and let them stand until they release their moisture, about 5 minutes. Then, squeeze the cucumber to remove any moisture and set aside. Tip: Salt draws out moisture through osmosis. This keeps the cucumber from releasing moisture into the salad and diluting the flavors.
  
• Cut 2 slices Black Forest ham into 1-inch (2.5-cm) thin strips and set aside.
  

To Assemble

• Add the vegetables, egg, and ham to the bowl of cooled potatoes and mix all together.
  
• Add 4 Tbsp Japanese Kewpie mayonnaise and combine well.
  
• Taste it and add more mayo, if you'd like. I added the remaining 2 Tbsp Japanese mayonnaise. Instead of adding more mayo, you can also add salt to bring out the flavor. I recommend chilling the potato salad in the fridge for 30–60 minutes before serving, but you could serve it immediately as well.
  

To Serve

• You can pair this versatile Japanese Potato Salad with just about anything. I like to serve it with Karaage (Japanese Fried Chicken) and Hambagu (Japanese Hamburger Steak). For a barbecue or potluck, see my list of Japanese recipes that go perfectly with this potato salad. It‘s a classic addition to your bento lunchbox, too! If you have leftovers, try making my childhood favorite Potato Salad Pork Rolls.
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 3–4 days or in the freezer for 2–3 months.